It has been reported that human leukemia virus, specifically, adult T-cell leukemia virus (referred to as ATLV hereinafter) is a retrovirus which is a case of human adult T-cell leukemia and that the provirus is integrated in the chromosome of tumor cells and cell lines established from leukemia patients (M. Yoshida, et al., Proc. Natl. Acad. Sci., USA 79, 2031, 1982). Therefore, clarification of the structure of human leukemia virus has been considered to greatly contribute to diagnosis, therapy and prevention of human leukemia and/or lymphoma. In this regard Oroszlan, et al. (Proc. Natl. Acad. Sci., USA, 79, 1291-1294, 1982) discloses the sequence of only 25 amino acids of viral protein p24 of a human leukemia virus called HTLV.